Regulations concerning the gathering of aggregate materials for use in concrete have been made more rigorous year after year to protect disasters, natural environments and the like. For this reason, there has been a rapid switch to sea sands for use as fine aggregates in place of mountain sands and river sands. Each year the amount of sea sands used increases.
In reinforced concrete structures and the like wherein sea sands are used, there is a problem that the steel materials used in concrete, such as reinforcing bars, steel frames, lathes and the like, are rusted and corroded by the chlorides contained in sea sands. There is generally about 0.1 to 0.4% salinity in sea sands which have not been desalted. Thus it is very dangerous to use such sea sands without any treatment, because the possibility of said problem will occur is exceedingly high. Therefore, it is necessary to regulate the maximum amount of chlorides contained in sea sands to be used in reinforced concrete structures and the like. According to the 1975 Revised Edition of JASS (Japanese Architectural Standard Specification), the maximum amount of chlorides is 0.1 percent by weight calculated in terms of sodium chloride based on an absolute dry amount.
To prevent the aforesaid problem caused by chlorides contained in sea sands, there are two methods; a flushing method and a method using a corrosion inhibitor. There is a greater tendency to employ the latter method because the former method requires a large amount of clear water and is not easily carried out.
The use of nitrites, dichromates or mixtures thereof (Japanese Patent Publication No. 8021/1969), the use of a mixture of sodium nitrite and calcium nitrite (Japanese Patent Publication No. 20260/1978) and the like are already known as corrosion-inhibiting methods. However, these methods only teach a corrosion-inhibiting effect for sodium chloride and calcium chloride and do not explain a corrosion-inhibiting effect for the wide variety of salts present in sea water. Generally nitrites do not have a sufficient corrosion-inhibiting effect unless a relatively large amount of nitrites relative to the chlorides is used. Dichromates being harmful to the human body are not preferable from the viewpoint of avoiding environmental pollution.
The present invention has been developed in order to solve the aforesaid problem. The gist of the invention is the use of corrosion inhibitor which not only has an excellent corrosion-inhibiting effect for steel materials but also has no bad side effects upon such properties of concrete or mortar as coagulation, hardening, size stability, durability and the like.